commit 8ebf5ceb0f5408d1ebc26c19702ac0762ef5ea04
author Ned Deily <nad@python.org> Wed May 23 21:55:15 2018 -0400
committer GitHub <noreply@github.com> Wed May 23 21:55:15 2018 -0400
tree eca9d86e7742c3ed4996506cfc7958b3582e07e6
parent 453bd0bc65b7ea6a18c43da69143ab10d54c0a35

bpo-33109: argparse subparsers are once again not required by default (GH-6919)

bpo-26510 in 3.7.0a2 changed the behavior of argparse to make
subparsers required by default, returning to the behavior of 2.7
and 3.2. The behavior was changed in 3.3 to be no longer required.
While it might make more sense to have the default to required,
compatibility with 3.3 through 3.6 is probably less disruptive
than trying to reintroduce compatibility with 2.7 at this point.
This change restores the 3.6 behavior.

Lib/argparse.py

diff --git a/Lib/argparse.py b/Lib/argparse.py
index e3da7f0..e0e367b 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1077,7 +1077,7 @@
                  prog,
                  parser_class,
                  dest=SUPPRESS,
-                 required=True,
+                 required=False,
                  help=None,
                  metavar=None):